1. Field of the Invention
The present invention relates to an optical semiconductor device and a fabrication method for the optical semiconductor device, preferably used for optical fiber communication systems and the like.
2. Description of the Related Art
In recent years, in accordance with improvement of optical communication modules smaller in size and lower in electric power consumption, optical devices, such as semiconductor lasers and/or optical modulators, able to operate even at high temperatures are demanded.
Conventional optical devices used for optical fiber communication systems have been made mainly of InGaAsP based materials.
Lately, optical devices made of AlGaInAs based materials that realize sufficient high-speed performance at a high temperature because of their superior band structure of hetero junctions have been developed.
Further, optical devices with buried heterostructure can reduce driving electric current and realize high-speed performance, and therefore have been focused on.
Here, FIG. 6 shows an example of a conventional buried heterostructure semiconductor laser (an optical semiconductor device) configured by AlGaInAs based materials.
A conventional buried heterostructure semiconductor laser made from AlGaInAs based materials, as shown in FIG. 6, includes an optical waveguide formed by sequentially depositing (stacking) an n-type InP lower cladding layer 101 also serving as a buffer layer, an AlGaInAs/AlGaInAs strained multiple quantum well active layer 102, a p-type InP upper cladding layer 103, and a p-type InGaAs contact layer 104 on an n-type InP substrate 100 and by processing the stacking body (the deposited layers) into a mesa shape, and has a structure that the opposite sides of the optical waveguide in a mesa shape are buried with an InP layer (here, a semi-insulating InP layer) 105. In FIG. 6, symbol 106 represents an n-electrode; symbol 107 represents a p-electrode; and symbol 108 represents a SiO2 film (layer)
Several fabrication methods for such a buried heterostructure semiconductor laser are proposed, but a buried heterostructure semiconductor laser is usually fabricated by the following method.
First of all, as shown in FIG. 7(A), the n-type InP lower cladding layer 101 also serving as a buffer layer, the AlGaInAs/AlGaInAs strained multiple quantum well active layer 102, the p-type InP upper cladding layer 103 and the p-type InGaAs contact layer 104 are stacked on the n-type InP substrate by carrying out crystal growth and the stacking body are processed into a mesa shape by etching.
After that, as shown in FIG. 7(B), an InP layer (in this case, a semi-insulating InP layer) is re-grown (formed) on opposite sides of the mesa structure by, for example, the MOCVD method, so that an InP burying layer (here, a semi-insulating InP burying layer) 105 is formed.
This fabrication method can flexibly deal with various waveguide shapes and can therefore have extremely wide applicability. This method is the most realistic when a semiconductor laser has a mesa body that is relatively high and is buried by a high-resistance semiconductor layer (here, a semi-insulting InP layer), which is suitable for high-speed operation, as shown in FIG. 6.
Japanese Patent Laid-Open No. HEI 8-172241 and Japanese Patent Laid-Open No. 2002-134842 concern buried heterostructure semiconductor lasers configured by AlGaInAs based materials.